By ozonizing (through ozone addition), long-chain, unsaturated compounds, ozonized products, specifically ozonides, can be manufactured, which can be subsequently cleaved into shorter chain fragments. Depending upon the type of ozonized product and the cleavage process, oxidative or reductive, the latter shorter chain fragments consist primarily of acids, aldehydes, ketones or alcohols. If, for example, commercial oleic acid (from olein) is treated with ozone, the ozonide produced decomposes exothermally (by adding oxygen) into pelargonic acid and azelaic acid. If olefins are ozonized, then on oxidative cleaving corresponding carboxylic acids and carbonyl compounds, and on reductive cleaving alcohols and carbonyl compounds, are produced.
The present invention applies to the ozonizing of unsaturated compounds, specifically olefins, including unsaturated carboxylic acids, with both one and more than one double bond. The process according to the invention and the device for implementing the process, however, do not cover the cleaving of the ozonized product. This cleavage step in any given case is the subject of a subsequent processing step and/or system.
The ozonization of unsaturated compounds can be described by the following reaction: ##STR1##
The reactive enthalpy (.delta.H) of this ozonizing reaction amounts to about 100 kcal/mol of double bonds or about 2,000 kcal/kg of reacted ozone. The elimination of this large amount of heat creates a great problem since the reaction is supposed to take place at a relatively low temperature in order to prevent a premature onset of ozonide cleaving. Ozonides are relatively unstable and already start to decompose at room temperature--this step equally being an exothermal reaction.
As mentioned, the ozonized product, in this case the ozonide, is cleaved only in a subsequent step. The splitting can be accomplished, e.g., oxidatively at about 100.degree. C., according to the following reaction: ##STR2##
To prevent a premature onset of this cleavage of the ozonide, a reactive solvent can be added to reaction (1), for example, an organic acid or alcohol, which converts ozonides to ester hydroperoxides and/or alkoxy hydroperoxides, which in turn are substantially more stable than the ozonides themselves. In the former case, e.g., the following reaction takes place: ##STR3##
The resulting ozonized products produced, in this case ester hydroperoxides and aldehydes, can be subsequently converted in a separate reaction step to corresponding acids by hydrolytic-oxidative fission. ##STR4##
After separation by distillation, the reactive solvent (R" COOH) can be returned to the process.
An effect of ozonization is that the viscosity of the ozonized product is considerably increased. The viscosity can be reduced, however, by the reactive solvent used for stabilization in reaction (3). U.S. Pat. No. 2,813,113, for example, teaches that in the ozonolysis of oleic acid the viscosity of the liquid phase in the ozonization reaction is reduced by adding pelargonic acid to the charge mixture. Following the oxidative splitting of the ozonide, both the added and the produced pelargonic acid are separated from the manufactured azelaic acid.
Aside from the problem of keeping the viscosity of the ozonized product at a low level, there is the requirement, as mentioned above, of removing the heat of reaction of the ozonization reaction, at least to the extent that the cleavage of the ozonized product, for example, the ozonide or ester hydroperoxide, is sufficiently delayed. For this purpose the reaction temperature, if possible, should not exceed about 50.degree. C.
To carry off the heat of the reaction by evaporation cooling means, it was proposed in U.S. Pat. No. 2,865,937 that from 100% to 600% of water be added to the organic charge mixture. The reaction heat is then eliminated by water evaporation and by the removal of water vapor together with waste gases. However, by means of the reaction heat, only about 4 kg of water per kg of reacted ozone are evaporated. The remaining water stays with the ozonized product and has to be evaporated at considerable expense. The problem is compounded by the fact that the specifically short-chain reaction products are volatile in the presence of water vapor. This produces not only a loss of acceptable products, but makes for additional air exhaust and/or waste water problems. Furthermore, according to data given in U.S. Pat. 2,813,113, the presence of a substantial volume of water (exceeding 10% to 15%) will have a negative effect on the ozonized product.
However, if the reaction heat is to be removed by indirect cooling according to U.S. Pat. No. 2,813,113, then because of the required low temperature of 25.degree. to 45.degree. C., a high expense in equipment, together with the high power and coolant water requirements, are needed for the removal of reaction heat.
Both for economic and engineering reasons a practically quantitative conversion of reactants is a basic requirement in the ozonization process. Primarily because of the danger of air pollution and the poisonous nature of ozone--the maximally tolerable working place concentration (MAC)=0.1 ppm--the entire quantity of ozone employed in the reaction should be used up to prevent it from being exhausted into the open air together with the waste gases. Otherwise, extensive ozone disposal installations would be required. Therefore, according to the known process of U.S. Pat. No. 2,813,113, a counterflow reactor is proposed, in which the liquid phase flows from top to bottom and the ozone containing gas from the bottom to the top. However, a counterflow reactor is very expensive for ozonizing because of the large gas-liquid ratio and the high viscosity of the ozonized product. Contrasted with such a counterflow reactor, a parallel or concurrent flow operation would make it feasible to allow a 20- to 30-fold greater gas velocity in the reactor, so that the latter paralleled flow reactor could be designed on a correspondingly smaller scale. But up until now no quantitative conversion of reactants has been successfully carried out with a parallel flow operation.